Standard procedures for preparing tissue samples for microscopic examination involve embedding the tissue sample in paraffin and slicing the paraffin-embedded tissue sample very thinly with a microtome. Prior to embedding the tissue sample, the tissue sample is pre-treated in various solutions appropriate to the examination. Typically, prior to paraffin embedding, the tissue sample is fixed, dehydrated, cleared, infiltrated with molten paraffin and, depending on the test, stained. Such prior treatment of the tissue sample requires subjecting the tissue sample to contact with various fluids, including ethanol, zylene, formaldehyde and water.
A histology laboratory processes a large number of tissue samples for examination and it is important that the tissues be prepared as efficiently as possible. A large variety of apparatus has been developed to improve the efficiency of the preparation process. U.S. Pat. No. 3,674,396 to McCormick discloses capsules in which a tissue sample is both prepared for embedding through exposure to various solutions and is then embedded within the capsule. The '396 McCormick patent discloses a process wherein the tissue sample is statically exposed to the various fluids required for preparation of the tissue samples. In the capsules of the '396 McCormick patent, perforated bottom walls are used to retain the tissue samples while providing access to the tissue samples of the various solutions and finally, to molten paraffin.
U.S. Pat. Nos. 4,557,903 and 4,569,647, both to McCormick, disclose improved apparatus for preparing and embedding tissue samples for histological examination. In the '903 McCormick patent, a tissue specimen processing capsule is provided which includes a pair of interlocking frames, each of the frames having a porous web spread across its central opening for holding a tissue specimen in a region divided between the webs. The porous webs permit access to the specimen by processing and impregnating fluids. After the tissue specimen is processed, it is removed from the capsule and placed in a depression of a mold. The empty capsule is placed over the mold depression containing the tissue specimen. Molten paraffin is poured into the mold to fill the depression and to cover the tissue specimen and the porous material of the capsule. The molten paraffin solidifies to form a tissue block with the capsule serving as a clampable base for an outwardly extending, tissue-containing portion.
The '647 McCormick patent discloses an improved method for contacting a tissue specimen with a fluid which is used to treat the tissue specimen. In the '647 McCormick patent, capsules for processing and embedding tissue samples each include a mold, which provides a cavity to receive the tissue sample. The mold has an upper end and a porous or non-porous bottom. The capsule further includes a cover which fits over the open upper end of the mold. The cover includes a frame on which is located a web of porous material intermediate the top and bottom of the frame so that the cover is provided with a recess. The porous web provides access to tissue processing liquids and liquid tissue embedding material, such as paraffin, but prevents passage of any small portions of the tissue specimen which may be generated, thereby preventing cross-contamination of individually capsuled and jointly processed tissue samples. After the tissue samples have been treated with the required fluids, the cover recess above the porous web is at least partially filled with molten paraffin embedding material so that when the embedding material solidifies, the porous web is embedded and the solidified material is thereby formed into a block in the mold. With the porous web and the tissue sample mutually embedded in the block of solidified paraffin, the block is removed from the mold and the cover may be clamped in a microtome and sliced by a microtome blade.
In one embodiment of the '647 McCormick patent, the capsules are adapted to form a stack and the molds are provided with porous bottoms that do not adhere to the embedding paraffin The stacked capsules provide a passageway running from top to bottom, defined by the molds and cover frames, for passage of a treating fluid in a direction orthogonal to the top and bottom of the capsules. The tissue samples held within the stack capsules are processed by flowing solutions through the passageway formed by the stacked capsules. A molten paraffin embedding material is finally introduced into the stacked capsules. When the stack is separated each tissue sample is embedded in a block of material that is attached to the respective covers.
While apparatus and methods for preparing and embedding tissue samples for histological examination have progressed over the years to provide for efficient methods and apparatus for preparing tissue specimens for histological examination, the large number of tissue samples which are prepared daily by a histological laboratory require the most efficient techniques available to increase the number of samples that can be processed.
Accordingly, it is a principal object of the present invention to provide a cassette for use in the treatment of tissue specimens for histological examination which increases the efficiency of treatment of a fluid specimen by various required fluids.
Another object of the present invention is to provide apparatus for the simultaneous treatment of multiple tissue specimens for histological examination.
Other objects of the invention include providing continuous flow systems and reciprocating flow systems for tissue processing liquids which recycle the various reagents that are used for processing tissue samples and in the economical use of processing cassette components in the final stage of tissue embedding and slicing.